1. Field of the Invention
The present invention relates to a micromachined structure and to an opto-mechanical switch (micro-switch) incorporating the micromachined structure. Specifically, it relates to a latching mechanism incorporated in the opto-mechanical micromachined switch.
2. Description of Related Art
Micromachines are small electromechanical devices that are fabricated on wafers of silicon and other materials using semiconductor manufacturing techniques. Optical switches in micro-electromechanical systems (MEMS) employ tiny mirrors that are etched onto silicon wafers. Such optical switches are commonly used in fiber-optic networks, through which light signals/data are routed. The tiny mirrors can be positioned to intercept the incoming light signals conveyed via the individual strands of optical fiber. Or alternatively, the mirrors can be pivoted to direct the incoming light beam at a desired angle into a receiving fiber.
Opto-mechanical switches typically include a light source, a light receiver, and a movable light blocking/reflecting mechanism. The light blocking/reflecting mechanism typically includes a drive motor that is selectively actuated to move a blocking/reflecting member (e.g., a mirror) between or among different positions, thereby performing the micro-switch function.
Typically, an electromagnetic drive motor is used to turn on/off the micro-switch by moving the mirror. In the past, to maintain the switch in the xe2x80x9conxe2x80x9d position, current must be applied continuously to maintain the electromagnetic force on the mirror. The continuously applied current inherently generates excess heat, which is dissipated to the neighboring structure, which is undesirable for a micro-electromechanical system. Among other things, this heat can cause the reflective surface and supporting structure to change shape and size, thereby increasing mechanical and optical instability. Besides, continuous application of electric current also results in high-energy consumption. This heating problem is exacerbated when a large number of micro-switches are used in a large array for switching in an optical network. It is therefore desirable to provide an opto-mechanical micromachined micro-switch that avoids the heating problems associated with the continuous application of electric current.
To overcome the shortcomings of existing optical switches described above, the present invention relates to an opto-mechanical micro-switch assembly that is more efficient, more mechanically and optically stable, and consumes less energy. Specifically, this invention relates to a novel magnetic latching mechanism for the mirror in the micro-switch. The present invention also relates to a method of operating the opto-mechanical micro-switch assembly.
According to one embodiment of the present invention, the overall assembly of a micromachined switch consists of an inner frame pivotally connected to an outer frame formed from a monocrystalline silicon substrate via torsion beams. The structure of the inner frame includes a light-reflecting (mirror) surface. A current can be applied to coils that are attached to the inner frame. Permanent magnets are attached onto the outer frame. Because of the interaction of the current and the magnetic field of the permanent magnets, an electromagnetic force causes the inner frame, and thereby the mirror, to pivot about the beams. When the mirror rotates to a certain position, the mirror surface intercepts (blocks or reflects) light transmitted via fiber optic networks. It is often required to maintain the mirror at such positions for a length of time during the operation of the micro-switch. The present invention provides a novel mechanism for latching the mirror for such purpose.
According to one embodiment of the present invention, a piece of magnetic material (e.g., PERMALLOY(trademark) magnetic material, hereinafter referred to in short as xe2x80x9cPermalloyxe2x80x9d) is attached to the lower portion of the moving/rotatable inner frame. The outer frame consists of layers of a silicon substrate, a permanent magnet, and a nickel/iron base. These layers are etched onto each other using prevailing art of micromachining. Upon applying an initial electro-magnetic force to rotate the inner frame past a threshold, the Permalloy piece is brought closer to the permanent magnet layer. Due to the attraction between the Permalloy piece on the inner frame and the permanent magnet layer in the outer frame, the inner frame of the opto-mechanical micro-switch can be latched onto the outer frame without continuous application of electric current to maintain electro-magnetic force to keep the inner frame in the rotated position.
In another embodiment of the present invention, a Permalloy piece is attached to the permanent magnet layer in the outer frame to focus the magnetic field at the Permalloy piece on the inner frame. During pivotal movements, the Permalloy piece already attached to the inner frame will be drawn to the Permalloy piece on the outer frame. The addition of the Permalloy piece on the outer frame increases the effective magnetic force, which attracts and holds the two Permalloy pieces in a latched-on position.
The above, as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.